This invention relates to paper webs and methods of making formed paper webs. In particular, this invention relates to disposable absorbent paper webs such as paper towels, wipes, tissues, and toilet tissue and methods of making such webs.
Disposable paper products such as paper towels, wipes, facial tissue, and toilet tissue have long been popular, primarily for single or limited use applications. Depending on the intended end use, paper products of this type generally require varying levels of softness, absorbency and strength. In addition to softness, absorbency and strength, the overall look, feel, and performance of disposable paper products is important, particularly in premium paper products.
Two important characteristics that contribute to the overall look, feel, and performance of disposable paper products are bulk and extensibility. Bulk is defined as the ratio of paper thickness to basis weight. Bulk may be increased by increasing the thickness, or caliper, of the paper, without increasing its basis weight, such as by embossing. Extensibility refers to the ability of paper to stretch significantly without tearing. Extensibility is not typically an attribute of uncreped paper webs, particularly tissue paper webs. Foreshortening of paper, such as by creping or wet microcontraction, may increase extensibility, but it also increases basis weight. Tissue paper webs generally have only a few percent elongation to break, due to the relatively inelastic nature of the constituent paper fibers. However, increasing the extensibility, and more preferably the elasticity, of paper webs would significantly enhance the overall look and feel of the paper web.
Increasing bulk without significantly increasing basis weight contributes to the texture and subjective softness of the paper by increasing its compressibility, resulting in a favorable tactile impression to the user. Increasing extensibility contributes to the overall look, feel, and performance of disposable paper products by increasing the subjective feeling of softness, or hand, of the web. In paper towels, wipes, and other paper products useful for scrubbing, increased extensibility also aids in preventing unwanted tearing of the sheet during use.
Paper webs produced on conventional papermaking machines are typically formed by depositing an aqueous slurry of paper fibers on a foraminous surface, such as one of a pair of converging Fourdrinier wires where initial dewatering and rearranging of fibers occurs. After the initial forming of the paper web on the Fourdrinier wires, the paper is transferred to a press dewatering felt for further drying by dewatering. Dewatering felts of conventional paper machines are typically made of tightly woven felt composed of very fine fibers of wool or synthetic material. To dewater the paper, the dewatering felt and paper are pressed between pairs of rolls running together, similar to the rolls on a wringer-type washing machine. The rolls often incorporate vacuum systems to more effectively draw water from the paper and the felt. Additional sheet compaction occurs as a pressure roll adheres the entire sheet area to a drying drum such as a Yankee dryer.
The compaction necessary to economically form and dry paper webs on conventional paper making machines causes such webs to have relatively low caliper, relatively high stiffness, and limited extensibility. Increasing caliper may be accomplished by increasing the amount of paper fibers in the starting furnish. But increasing caliper in this manner simply increases basis weight correspondingly, and therefore does not increase bulk or decrease relative stiffness.
In recent times various modifications and improvements to conventional paper making machines have been made to make bulkier and somewhat more extensible disposable paper products. One significant improvement to the manufacturing process, which yields a significant improvement in the resulting consumer products, is the use of through-air-drying to replace conventional press felt dewatering. In through-air-drying, like press felt drying, the web begins on a forming wire which receives an aqueous slurry of less than one percent consistency (the weight percentage of fibers in the aqueous slurry) from a headbox. Initial dewatering takes place on the forming wire. From the forming wire, the web is transferred to an air pervious through-air-drying belt. This xe2x80x9cwet transferxe2x80x9d occurs at a pickup shoe, at which point the web may be molded to the topography of the through air drying belt.
Over time, further improvements became necessary. A significant improvement in through-air-drying belts is the use of a resinous framework on a reinforcing structure. The resinous framework generally has a first surface and a second surface, and deflection conduits extending between these surfaces. The deflection conduits provide areas into which the fibers of the web can be deflected and rearranged. This arrangement allows drying belts to impart continuous patterns, or, patterns in any desired form, rather than only the discrete patterns achievable by the woven belts of the prior art. Examples of such belts and the cellulosic fibrous structures made thereby can be found in U.S. Pat. No. 4,514,345, issued Apr. 30, 1985 to Johnson et al.; U.S. Pat. No. 4,528,239, issued Jul. 9, 1985 to Trokhan; U.S. Pat. No. 4,529,480, issued Jul. 16, 1985 to Trokhan; and U.S. Pat. No. 4,637,859, issued Jan. 20, 1987 to Trokhan. The foregoing four patents are incorporated herein by reference for the purpose of showing preferred constructions of patterned resinous framework and reinforcing type through-air-drying belts, and the products made thereon. Such belts have been used to produce extremely commercially successful products such as Bounty paper towels and Charmin Ultra toilet tissue, both produced and sold by the instant assignee.
Still another improvement to the papermaking process involves a special papermaking apparatus that provides a paper web having multiple basis weight regions. Such a process is described in U.S. Pat. No. 5,245,025, issued Sep. 14, 1993 to Trokhan et al.; U.S. Pat. No. 5,503,715, issued Apr. 2, 1996 to Trokhan et al.; and U.S. Pat. No. 5,534,326, issued Jul. 9, 1996 to Trokhan et al.; the disclosure of each of which is hereby incorporated herein by reference.
All of the above mentioned improvements to conventional papermaking to make bulkier and somewhat more extensible disposable paper products involve significant modifications to existing equipment and machinery. Although the added bulk, with its accompanying characteristics of texture and softness, is desirable, the capital costs associated with modifying a conventional papermaking machine to incorporate the necessary improvements are often prohibitive.
In both conventional and nonconventional paper making a certain level of extensibility is typically produced in paper by a foreshortening operation after drying the paper. While foreshortening can take a number of forms, creping is the most common form. Creping typically occurs as one of the last steps in the paper making process as the formed, dry paper is removed from a drying drum by a doctor blade. In a simplistic view, creping forms a pattern of microscopic ridges and folds transverse to the machine direction of the web. The frequency and amplitude of the microscopic accordion-like folds can be varied somewhat within narrow operating ranges, and the resulting web only gains extensibility in the machine direction. Extensibility in the cross direction remains virtually unchanged, being only a few percent tensile elongation to break. In addition, the creping process increases the basis weight of the web proportional to the amount of creping. Therefore, a given level of crepe-induced extensibility is accompanied by a proportional increase in basis weight.
Increasing the caliper and bulk of paper webs produced on either conventional or non-conventional papermaking machines may also be achieved in post-paper making converting operations. Converting operations refer to further processing of finished paper into different forms, such as by embossing, printing, and packaging. For example, higher caliper can be achieved by laminating single plies of paper into multi-ply products, and higher bulk can be achieved by embossing. Bulk and caliper can be increased by a combination of embossing and laminating. However, conventional embossing, particularly macro-pattern embossing, requires a relatively stiff sheet to retain the embossing pattern. Also, conventional macro-pattern embossing typically has little effect on paper extensibility, and virtually no effect on paper elasticity. By xe2x80x9cmacro-pattern embossingxe2x80x9d is meant embossing which forms patterns easily distinguishable by the human eye when observed from a distance of approximately 12 inches.
Accordingly, there is a need for a means of economically converting paper webs, particularly webs made on conventional paper making machines, into paper webs having increased bulk, texture, and good overall look and feel, together with increased extensibility in at least one direction.
Additionally, it would be desirable to have disposable paper products with increased bulk, texture, and good overall look and feel, together with increased extensibility and elasticity in at least one direction.
Further, it would be desirable to be able to produce paper webs having increased bulk, texture, and good overall look and feel, in a post-papermaking operation that does not require capital expenditures to modify an existing papermaking machine.
A paper web of the present invention has a longitudinal centerline and a transverse centerline, and comprises a plurality of first regions and a plurality of second regions. The first regions form boundaries separating the second regions, the first regions being substantially in a plane of the paper web. The second regions comprise a plurality of raised out-of-said-plane rib-like elements, the rib-like elements of each second region being disposed parallel to a major rib axis and perpendicular to a minor rib axis. All or most of each first regions have both major rib axis and minor rib axis components. The first and second regions undergo geometric deformation when the web material is subjected to an applied elongation along at least one axis.
A method of the present invention comprises the steps of providing a cellulosic substrate; providing a first platen comprising toothed regions and untoothed regions; providing a second platen comprising toothed regions, the second platen being aligned with the first platen such that the toothed regions of the first and second platens mesh when operably engaged; and pressing the cellulosic substrate between the first platen and the second platen such that the toothed regions deform said web to form regions of discrete fan-folded rib-like elements. Optionally, the cellulosic substrate can be moistened prior to the pressing step.